The present invention relates generally to sealed bearing earth boring drill bits, such as rotary cone rock bits. More particularly, the present invention relates to the seals that are used to seal the bearing area between the bit leg and the rolling cone. Still more particularly, the present invention relates to a seal that is canted or angled with respect to the bearing axis and also to a canted leg/cone interface.
An earth-boring drill bit is typically mounted on the lower end of a drill string and is rotated by rotating the drill string at the surface or by actuation of downhole motors or turbines, or by both methods. With weight applied to the drill string, the rotating drill bit engages the earthen formation and proceeds to form a borehole along a predetermined path toward a target zone typical earth-boring bit includes one or more rotatable cutters, or cones. The cutters roll and slide upon the bottom of the borehole as the bit is rotated, thereby engaging and disintegrating the formation material in the bit""s path. The rotatable cutters may be described as generally conical in shape and are therefore sometimes referred to as rolling cones.
Bits designed to work with rolling cones typically include a bit body with a plurality of journal segment legs. The rolling cones are mounted on bearing pin shafts that extend downwardly and inwardly from the journal segment legs. The borehole is formed as the gouging and scraping or crushing and chipping action of the rotary cones removes chips of formation material. The chips are carried upward and out of the borehole by drilling fluid that is pumped downwardly through the drill pipe and out of the bit. The drilling fluid carries the chips and cuttings in a slurry as it flows up and out of the borehole.
In a typical bit, the earth-disintegrating action of the rolling cone cutters is enhanced by providing the cones with a plurality of cutting elements. Cutting elements are generally of two types: inserts formed of a very hard material, such as tungsten carbide, that are press fit into undersized apertures in the cone surface; or teeth that are milled, cast or otherwise integrally formed from the material of the rolling cone.
The cost of drilling a borehole is proportional to the length of time it takes to drill to the desired depth and location. The time required to drill the well, in turn, is greatly affected by the number of times the drill bit must be changed in order to reach the targeted formation. This is the case because each time the bit is changed, the entire string of drill pipe, which may be miles long, must be retrieved from the borehole, section by section. Once the drill string has been retrieved and the new bit installed, the bit must be lowered to the bottom of the borehole on the drill string, which again must be constructed section by section. This process, known as a xe2x80x9ctripxe2x80x9d of the drill string, requires considerable time, effort and expense. Accordingly, it is always desirable to employ drill bits that will drill faster and longer without failing.
The length of time that a drill bit can be employed before it must be replaced depends on many factors, not the least of which is its ability to resist the wear associated with drilling. All of the components of a bit are subjected to severe wear, as a result of frictional contact with the formation and the drilling fluid. While wear can damage any surface of the bit, the bearing surfaces of the bit, namely those between each journal segment and its associated cone, are particularly vulnerable. If grit or other particles were to enter the annular space between the cone and the journal while the bit was rotating, the bearing surfaces would be quickly destroyed, rendering the bit unusable.
For this reason, a great deal of attention has been given to providing a sealing system that prevents the ingress of particles to the bearing surface. It is desirable to provide a sealing system that does not take up too much of the available space on the bit leg, yet provides a good seal. It is further desired to provide a bit that has superior wear resistance and can accommodate additional wear resisting features.
The present invention provides a sealing system that prevents the ingress of particles to the bearing surface and does not take up too much of the space needed for the bearings. The present invention further results in a bit that has superior wear resistance and can accommodate additional wear resisting features. In one preferred embodiment, the present bit includes a canted bearing seal whose operating axis is neither parallel nor perpendicular to the bearing axis. The canted bearing seal can be used alone or in combination with additional canted or conventional seals. In another embodiment, the present invention includes a bit having a canted interface between the bit leg and the cone backface. In still another embodiment, the present invention includes a bearing seal that is mounted in a groove in the cone and a corresponding cut-out in the leg, so that there is no straight-line path past the seal.
One embodiment of the present invention comprises bit that comprises a bit body having at least one leg having a journal segment extending inwardly and downwardly therefrom and at least one rolling cone cutter rotatably mounted on the bit body and having a generally conical outer surface and a cone backface. The leg includes a shirttail, and the shirttail has an outer surface and a leg backface that defines an interface with said cone backface and the leg backface is canted.
In another embodiment, the present bit comprises a bit body and at least one rolling cone cutter rotatably mounted on said bit body. The body has at least one leg having a journal segment extending inwardly and downwardly therefrom, the leg including a shirttail, and the shirttail having an outer surface and a canted leg backface. The rolling cone cutter has a generally conical outer surface and a cone backface, and the backface defines an interface with the shirttail inner surface and a seal is positioned in said interface. This embodiment can be used with a recessed or non-recessed shirttail and a convention or a non-positive seal.
Still another embodiment comprises a bit body, at least one rolling cone cutter rotatably mounted on said bit body. The body having at least one leg having a journal segment extending inwardly and downwardly therefrom, said leg including a shirttail, said shirttail having an outer surfaces and a leg backface. The rolling cone cutter has a bearing axis, a generally conical outer surface, and a cone backface. The cone backface defines an interface with said shirttail inner surface and a canted seal is positioned in the interface. The seal has an operating axis that is a canted with respect to said bearing axis.